Cyclic fatigue resistance of Reciproc Blue instruments used with different motions under controlled temperature conditions

Aim To evaluate the effect of different motions on the cyclic fatigue resistance of Reciproc Blue reciprocating files simulating the temperature of the clinical environment. Methodology After sample size calculation considering preliminary experimental data (a=0.05; b=0.20; d=30.0; r=32.0), 69 new R25 Reciproc Blue files were divided into three groups of 23 files each according to the tested motion: continuous rotation at 300 rpm, “RECIPROC” mode, and “WAVEONE” mode. All files were activated until fracture inside a stainless-steel artificial canal with 60° angle and 5 mm radius of curvature. The temperature was kept at 35°C and controlled with an internal thermometer inside the testing device. For each file, a single blinded operator measured the time to failure with a digital chronometer and the length of the fractured fragment with a digital calliper. A qualitative fractographic analysis was performed by observing the surface of the fractured files at the scanning electron microscope. The scalar data were tested for the assumptions for using parametric tests and then underwent a statistical analysis with a oneway analysis of variance and Tukey post hoc test (P = 0.05). Results The shortest lifespan of the files was registered in the continuous rotation group (204.1 24.2 s to failure). Both reciprocating motions led to significantly improved fatigue resistance. The “RECIPROC” mode performed better than the “WAVEONE” mode, exhibiting 329.8 31.5 s and 252.9 43.7 s to failure, respectively. No difference in fragment length was observed, confirming the correct positioning of the files inside the artificial canal. The scanning electron microscopic analysis confirmed that all the observed specimens fractured due to cyclic fatigue. Conclusions The results of the present study seem to encourage the use of R25 Reciproc Blue files preferably with their native motion to reduce the fracture risk in the clinical setting.